O-RADS Classification System
O-RADS (Ovarian-Adnexal Reporting and Data System) is a standardized ultrasound-based risk stratification system developed by the American College of Radiology that categorizes ovarian and adnexal masses into six risk categories (0-5) based on malignancy probability, with each category having specific management recommendations. 1, 2
System Overview and Purpose
The O-RADS system provides a universally recognized reporting tool using common terminology and a management framework for all categories of risk in ovarian and adnexal lesions. 1 The system was developed for average-risk patients and maximizes sensitivity rather than specificity to avoid missing ovarian cancer, which has low prevalence but is potentially highly lethal. 1
The Six Risk Categories
O-RADS 0: Incomplete Evaluation (No Risk Assessment)
- Represents incomplete evaluation due to technical factors such as bowel gas, large lesion size, adnexal location, or inability to tolerate endovaginal imaging. 1
- Management: Repeat ultrasound is recommended, or consider alternative imaging such as MRI in selected cases. 1
O-RADS 1: Physiologic Category (0% Malignancy Risk)
- Applies only to premenopausal women with normal ovarian findings consistent with normal physiology. 1, 2
- Includes follicles (simple cysts <3 cm) and corpus luteum (thick-walled cysts <3 cm with crenulated inner margins, internal echoes, and intense peripheral color Doppler flow). 1
- Management: No follow-up required. 2
O-RADS 2: Almost Certainly Benign (<1% Malignancy Risk)
- Includes simple cysts, non-simple unilocular cysts with smooth walls, and classic benign lesions (hemorrhagic cysts, dermoid cysts, endometriomas, paraovarian cysts, peritoneal inclusion cysts, hydrosalpinges). 1, 3, 2
Management varies by lesion type and patient menopausal status: 3
Premenopausal women:
- Simple cysts ≤3 cm: No follow-up needed. 3
- Simple cysts >3 cm to ≤5 cm: No additional management required. 3
- Simple cysts >5 cm but <10 cm: Follow-up ultrasound in 8-12 weeks. 3
Postmenopausal women:
- Simple cysts ≤3 cm: No follow-up needed. 3
- Simple cysts >3 cm but <10 cm: Follow-up in 1 year, with consideration of annual follow-up for up to 5 years if stable. 3
Classic benign lesions:
- Hemorrhagic cysts <5 cm: Refer to US specialist, gynecologist, or MRI; those >5 cm but <10 cm require follow-up in 8-12 weeks with referral if persistent or enlarged. 3
- Dermoid cysts <10 cm: Refer to US specialist, gynecologist, or MRI, with annual ultrasound follow-up if not surgically removed. 3
- Endometriomas <10 cm: US specialist or MRI evaluation if enlargement, changing morphology, or developing vascular component. 1, 3
- Simple paraovarian cysts: No follow-up, with optional single follow-up study in one year. 3
- Hydrosalpinx (any size): Refer to gynecologist. 1, 3
O-RADS 3: Low Risk (1% to <10% Malignancy Risk)
- Includes unilocular smooth cysts ≥10 cm, unilocular cysts with irregular inner wall, and multilocular smooth cysts with 1-3 locules <10 cm. 1, 2
- Also includes smooth solid lesions with color score 1. 1
- Management: Gynecologist consultation recommended. 2
O-RADS 4: Intermediate Risk (10% to <50% Malignancy Risk)
- Includes multilocular smooth cysts >10 cm or with color score 4, multilocular cysts with irregular inner walls, unilocular-solid lesions without papillary projections or with 1-3 papillary projections, multilocular-solid lesions with color score 1-2, and smooth solid lesions with color score 2-3. 1, 2
- Management: Gynecologist or gynecologic oncologist consultation recommended. 2
O-RADS 5: High Risk (≥50% Malignancy Risk)
- Includes unilocular-solid with ≥4 papillary projections, multilocular-solid with color score 3-4, solid lesions (≥80%) with smooth contour and color score 4, solid or solid-appearing (≥80%) with irregular contour, and presence of ascites and/or peritoneal nodules. 1, 2
- Management: Gynecologic oncologist consultation recommended. 2
Key Technical Considerations
- The system is based on transvaginal sonography, augmented by transabdominal or transrectal sonography as needed. 1
- Lesion size should be measured by the largest diameter regardless of the plane. 1
- For multiple or bilateral lesions, each lesion should be characterized separately, with management driven by the lesion with the highest O-RADS score. 1, 2
- The system applies only to lesions involving the ovaries or fallopian tubes (with exceptions for paraovarian cysts and peritoneal inclusion cysts). 1
Important Caveats
The system is designed for average-risk patients without acute symptoms and without substantial risk factors for ovarian cancer (such as significant family history or BRCA gene mutation). 1 Management may be modified by professional judgment regardless of O-RADS recommendations. 1
The O-RADS classification is not a substitute for thorough history and physical examination. 1 CA-125 levels are not routinely incorporated into the risk stratification system, as they may be misleading in certain contexts (elevated in premenopausal women with endometriosis, normal in some postmenopausal women with malignancy). 1
A key limitation is that the risk stratification is based on a database including only surgically managed lesions, which may overestimate malignancy risk in more benign categories. 1